Reduce subscription Profile-Update-Interval to 2 hours

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/PnvPanel.Api/Endpoints/SubscriptionEndpoints.cs

@@ -45,7 +45,7 @@ public static class SubscriptionEndpoints
             "Subscription-Userinfo",
             $"upload={result.Value.UsedUpBytes}; download={result.Value.UsedDownBytes}; total={total}; expire={expire}"
         );
-        response.Headers.Append("Profile-Update-Interval", "12");
+        response.Headers.Append("Profile-Update-Interval", "2");
 
         return Results.Text(base64Body, "text/plain; charset=utf-8");
     }